Conventionally, there is known the technique for utilizing a smartphone as a cordless extension unit of a fixed telephone (for example, see Patent Document 1). The Patent Document 1 discloses the technique related to an SIP (Session Initiation Protocol) client application. The SIP client application is operated on the smartphone, and the smartphone is extension accommodated as an SIP terminal in an SIP control unit incorporated in a network termination device such as a home gateway and an outgoing call, an incoming call, a telephone call or the like can be performed by the smartphone.
A smartphone in which the SIP client application is operated is registered as a cordless extension unit of a house telephone in the SIP control unit. The SIP control unit transmits an incoming call signal to the SIP client application on the smartphone when a call arrives. The SIP client application receiving the incoming call signal presents the incoming call to a user, and the user starts a telephone call. In order to use the smartphone as the cordless extension unit, thus, it is necessary to install the SIP client application into the smartphone, thereby performing various setting required for the SIP control unit.
Patent Document 1: Japanese Laid-open Patent Publication No. 2014-3363